Power-Line Communication (PLC) systems are useful for some specialized smart-grid applications such as to send meter readings back to a central office, or to send commands to control electrical distribution and loading. Home automation and networking can also use PLC with adapters inserted into ordinary A.C. power receptacles. PLC networking such as the HomePlug AV standard does not disturb the A.C. power distribution.
While PLC has been used for some time, low data rates (narrow-band) have been used. Half-duplex operations are used since transmission and reception cannot be done simultaneously. It is desired to carry higher data rates with PLC and to improve reliability.
FIG. 1 shows a PLC system. Power line 10 carries alternating current (A.C.) such as 110 volts, 120 volts, 220 volts, or 240 volts, alternating at 60 cycles per second, (60 Hz) or alternating at 50 Hz. Appliances, lamps, and other devices requiring electricity can be plugged into receptacles 12, 14, 16, 18. Communication signals between device 22 and personal computer (PC) 24 may be carried over power line 10 by special adapters plugged into receptacles 14, 16. However, when large load appliance 26 is switched on, it suddenly draws a large current from its receptacle 18. This large load can cause noise on power line 10 that can interfere with communications between device 22 and PC 24.
FIG. 2 shows noise that disrupts some sub-carrier frequencies during Power-Line Communication (PLC). Sub-carriers 20 are frequencies that a PLC transmits over. The same data may be simultaneously transmitted over several sub-carriers 20 to provide redundancy and mitigate the noisy A.C. power-line environment. Static noise 34 on the power line interferes with the signal being carried by sub-carriers 21, but not with other sub-carriers 20. Data can still be carried by other sub-carriers 20.
FIG. 3 illustrates a variety of noise types in PLC. Static noise 34 occurs at specific frequencies for long periods of time. Periodic noise 30 are impulses synchronized to the A.C. power cycle and may appear for long periods of time and then disappear for long periods of time, such as when a noisy appliance is turned on and then off. Aperiodic impulsive noise 32 is not synchronous with the A.C. power cycle but repeatedly appears. Asynchronous noise impulse 38 appears once and then disappears. Background noise may also exist across all frequencies.
The power line environment is inherently noisy with a variety of noise generators and sources. Noise may appear periodically or seemingly at random, and at any frequency. A different snapshot in time would show a different arrangement of noise and frequency than shown in FIG. 3.
It is desired to extend narrow-band PLC to a broad-band PLC with higher data rates. It is desired to detect and filter out noise on the power lines to allow data to be transmitted over low-noise frequencies. It is desired to dynamically detect noise and continuously adjust filtering to avoid noisy frequencies. It is desired to resume using frequencies that had noise that has now diminished to provide as many frequencies for data transmission as possible.